Liquid Crystal Testing Apparatus and Method for Image Capture Devices

ABSTRACT

A testing apparatus ( 100 ) for an image capture device ( 401 ) includes a liquid crystal device ( 101 ). The liquid crystal device ( 101 ) includes an array of pixels ( 102 ), which may actively or passively be changed from a transparent state to an opaque or semi-opaque state. The array of pixels are capable of segmentation into a plurality of predefined regions ( 107 ), which may be columns ( 108 ) or rows ( 208 ). A liquid crystal device driver ( 105 ) is configured to actuate the predefined regions ( 107 ), individually and sequentially, in a sweep pattern across the liquid crystal device. The testing apparatus ( 100 ) may be used to measure a variety of parameters associated with image capture devices, including exposure duration, continuous shutter frequency, and flash-shutter lag. The testing apparatus ( 100 ) is capable of operation in a variety of ambient lighting conditions.

BACKGROUND

1. Technical Field

This invention relates generally to test equipment for image capturedevices, and more specifically to a liquid crystal testing apparatus forimage capture devices, where the liquid crystal apparatus is disposedbetween an image capture device and a subject.

2. Background Art

Photography is experiencing an explosion in popularity due to advancesin technology. Digital cameras and digital imaging are fueling a newinterest in photography. Not too long ago, the only way to capture animage was to use a film camera. A user adjusted and aimed the camera ata subject, and then took the picture. The user then had no idea what thepicture looked like until they removed the film from the camera, tookthe film to a processing center, and had the film developed.

Digital cameras have revolutionized photographic process. With a digitalcamera, one points and shoots, seeing the image appear instantly on adisplay without the need of developing film. What's more, when thepicture fails to turn out as planned, the user simply deletes theelectronic image from memory and shoots again. The efficiency and lowcost associated with digital photography is very appealing to consumers.It is so appealing, in fact, that digital cameras are showing up on alltypes of electronic devices, including mobile telephones.

With the wide variety of digital camera manufacturers and devices, it issometimes difficult to compare “apples to apples” when purchasing adigital camera, or an electronic device having an integrated digitalcamera. Often, the specifications for each digital camera includedifferent measurements or test conditions, making it difficult for aconsumer to determine how the digital camera will perform in the realworld. One reason for this difficulty is the fact that there is no testequipment available that is capable of measuring digital cameraperformance data, including exposure duration, frame rate, and flashshutter lag, in a variety of lighting conditions. While some specializedequipment is capable of making these measurements in a low-lightlaboratory, such measurements are often not indicative of, for example,the digital camera's performance in broad daylight. The discrepancy maybe due to a variety of factors, including integrated metering,electronic device characteristics, and so forth.

There is thus a need for a testing apparatus for image capture devicesthat is capable of operation in bright light, as well as low light,conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a liquid crystal testing apparatusfor image capture devices in accordance with the invention.

FIG. 2 illustrates an alternate embodiment of a liquid crystal testingapparatus for image capture devices in accordance with the invention.

FIG. 3 illustrates another alternate embodiment of a liquid crystaltesting apparatus for image capture devices in accordance with theinvention.

FIG. 4 illustrates one embodiment of an image capture testing apparatusin accordance with the invention.

FIG. 5 illustrates a series of exemplary images that may be captured byan image capture device using a liquid crystal testing apparatus inaccordance with one embodiment of the invention.

FIG. 6 illustrates one embodiment of a method for determining acontinuous shutter rate associated with an image capture device by usinga liquid crystal testing apparatus in accordance with the invention.

FIG. 7 illustrates one embodiment for determining duration of exposurein an image capture device by using a liquid crystal testing apparatusin accordance with the invention.

FIG. 8 illustrates one embodiment of a method for determining flashshutter lag in an image capture device by using a liquid crystal testingapparatus in accordance with the invention.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove understanding of embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments resideprimarily in combinations of method steps and apparatus componentsrelated to testing image capture devices with a liquid crystal testingapparatus. Accordingly, the apparatus components and method steps havebeen represented where appropriate by conventional symbols in thedrawings, showing only those specific details that are pertinent tounderstanding the embodiments of the present invention so as not toobscure the disclosure with details that will be readily apparent tothose of ordinary skill in the art having the benefit of the descriptionherein.

It will be appreciated that embodiments of the invention describedherein may be comprised of one or more conventional processors andunique stored program instructions that control the one or moreprocessors to implement, in conjunction with certain non-processorcircuits, some, most, or all of the functions of testing image capturedevices with a liquid crystal testing apparatus in accordance withembodiments of the invention. The non-processor circuits may include,but are not limited to, software modules, communication circuits, signaldrivers, clock circuits, power source circuits, and user input devices.As such, these functions may be interpreted as steps of a method toperform image capture device testing by using a liquid crystal testingapparatus. Alternatively, some or all functions could be implemented bya state machine that has no stored program instructions, or in one ormore application specific integrated circuits, in which each function orsome combinations of certain of the functions are implemented as customlogic. Of course, a combination of the two approaches could be used.Thus, methods and means for these functions have been described herein.Further, it is expected that one of ordinary skill, notwithstandingpossibly significant effort and many design choices motivated by, forexample, available time, current technology, and economicconsiderations, when guided by the concepts and principles disclosedherein will be readily capable of generating such software instructionsand programs and circuits with minimal experimentation.

Embodiments of the invention are now described in detail. Referring tothe drawings, like numbers indicate like parts throughout the views. Asused in the description herein and throughout the claims, the followingterms take the meanings explicitly associated herein, unless the contextclearly dictates otherwise: the meaning of “a,” “an,” and “the” includesplural reference, the meaning of “in” includes “in” and “on.” Relationalterms such as first and second, top and bottom, and the like may be usedsolely to distinguish one entity or action from another entity or actionwithout necessarily requiring or implying any actual such relationshipor order between such entities or actions. Also, reference designatorsshown herein in parenthesis indicate components shown in a figure otherthan the one in discussion. For example, talking about a device (10)while discussing figure A would refer to an element, 10, shown in figureother than figure A.

Turning now to FIG. 1, illustrated therein is one embodiment of atesting apparatus 100 for testing image capture devices in accordancewith the invention. The testing apparatus 100 includes a liquid crystaldevice 101 comprising an array of pixels 102. The liquid crystal device101 is a panel or display that may be changed from a translucent to anopaque or semi-opaque state. For example, in one embodiment, the liquidcrystal device 101 is transparent when the array of pixels 102 isunactuated, and is opaque when the array of pixels is actuated. Theliquid crystal device 101 has an associated device width 103 and adevice length 104. The liquid crystal device 101 may be one of a varietyof types of liquid crystal devices, including STN, TN, cholesteric andpolymer dispersed liquid crystal devices. The liquid crystal device 101may be active or passive.

A liquid crystal device driver 105 is included in the testing apparatus100 for controlling the liquid crystal device 101. The liquid crystaldevice driver 105 is configured to actuate a plurality of subsets ofpixels in the array of pixels 102, individually, at any given moment intime. In one embodiment, the liquid crystal device driver 105 isconfigured to actuate a plurality of subsets 106 of the array of pixels102 as predefined regions, where predefined regions 107 are groups ofpixels forming either “bars” or “rows”. The bars are columns 108 havinga predetermined column width 109 and a predetermined column length 110.Turning briefly to FIG. 2, rows 208 have a predetermined row width 209and a predetermined row length 210. The columns 108 run the devicelength 104 of the liquid crystal device 101, while the rows 208 run thedevice width 103 of the liquid crystal device 101. While bars or rowswill be described and illustrated herein, it will be clear to those ofordinary skill in the art having the benefit of this disclosure that theinvention is not so limited. Other subsets of pixels, including circles,squares, and non-standard geometric shapes may also be used.

In one embodiment, the liquid crystal device driver 105 actuates thepredefined regions 107 individually and sequentially in a sweep pattern.The liquid crystal device driver 105 actuates a first predefined region,then a second predefined region, then a third, and so forth,sequentially, such that the actuated predefined regions pass across theliquid crystal device 101 in a wave-like or sweeping pattern. While thepredefined regions 107 are actuated individually, the duration ofactuation may be of a length such that multiple predefined regions 107are actuated simultaneously.

The predefined regions 107 are actuated in accordance with an inputfrequency received from an adjustable frequency generator 111. Theadjustable frequency generator 111 delivers the input frequency to theliquid crystal device driver 105. The input frequency determines howfast the predefined regions 107 sweep across the liquid crystal device101. The adjustable frequency generator 111 may be a standalone device.It may also be integrated with the liquid crystal device driver 105. Itmay be controllable by a computer 112, and may also be responsive to aphotodetector 113. In one embodiment, where the adjustable frequencygenerator 111 is responsive to the photodetector 113, a flash operatingat a flash frequency, either coupled to an image capture device orindependent as a separate strobe, is capable of altering the inputfrequency such that the input frequency is proportional to the flashfrequency received by the photodetector 113. Such an embodiment isuseful in synchronizing the testing apparatus 100 and image capturedevice as will be described below.

The testing apparatus 100 may be used to measure characteristics ofimage capture devices, including exposure duration, continuous shutterspeed, and flash-shutter lag. Many of these measurements, as describedbelow, are made by placing a subject on one side of the liquid crystaldevice 101, and then placing the image capture device on the other. Asthe liquid crystal device 101 is translucent in one embodiment, when thearray of pixels 102 is not actuated, the testing apparatus 100 iscapable of making these measurements in ambient lighting conditions, beit bright or low-level lighting.

Once the subject and image capture device are in position, the imagecapture device begins taking pictures of the subject. Once the testingapparatus 100 and image capture device are synchronized, measurementsmay be obtained by counting the predefined regions 107 appearing inimages. Thus, in some testing, the dimensions of the predefined regions107 become important. For example, in measuring exposure duration, wherethe predefined regions 107 comprise columns 108, column widths less thanor equal to the product of the device width 103, input frequency, andexposure time measurement resolution may be used to obtain accurateresults in a variety of lighting conditions. Experimental testing hasshown that an exposure time measurement resolution of between 1millisecond and 1 second works well in making this measurement.

Turning briefly to FIG. 3, the liquid crystal device 101 mayadditionally include graphical indicia 301 disposed thereon. Thegraphical indicia 301 may be printed on the surface of the liquidcrystal device 101, or may be generated by the actuation of selectedpixels from the array of pixels (102). By way of example, the graphicalindicia 301 may include instructions on using the device. The liquidcrystal device driver (105) may present a user with instructions priorto using the device. Alternatively, the graphical indicia 301 maycomprise a test pattern, such as a Macbeth table, suitable for use intesting image capture devices.

Turning now to FIG. 4, illustrated therein is a system 400 for measuringa parameter, such as duration of exposure or continuous shutter speed,associated with an image capture device 401 in accordance with oneembodiment of the invention. In the system, an image capture device 401is placed on one side of the liquid crystal device 101, while a subject402 is placed on the other. The image capture device 401 may include aflash 403.

The liquid crystal device driver (105) begins sweeping the predefinedregions 107 across the liquid crystal device 101 at the input frequency.The image capture device 401 begins capturing images of the subject 402through the liquid crystal device 101. Once the image capture device 401and the liquid crystal device 101 are synchronized, as will be describedbelow with FIG. 5, a variety of measurements may be made. For example,exposure duration may be measured by counting the number of predefinedregions 107 appearing in an image and multiplying the number by a periodassociated with each predefined region 107. Additionally, shutterfrequency may be measured by synchronizing the liquid crystal device 101with the image capture device 401 and determining the input frequency.

Turning now to FIG. 5, illustrated therein is a series of imagescaptured by the image capture device (401) configured as shown in FIG.4. The image capture device (401) is capturing images of the subject 402through the liquid crystal device (101). The liquid crystal devicedriver (105) is sweeping the predefined regions 107 across the liquidcrystal device (101) at the input frequency.

As mentioned above, to make some measurements, the image capture device(401) needs to be synchronized with the liquid crystal device (101). Oneway to do this is by capturing a series of images501,502,503,504,505,506 and adjusting the adjustable frequency generator(111) until at least one of the predefined regions 107 is active atsubstantially the same position in at least two consecutive images505,506 from the series of images 501,502,503,504,505,506. Then,selecting one image from the two consecutive images 505,506, themeasurement may be made.

Image 501 shows the subject with the predefined regions 107 sweepingacross the liquid crystal device (101). When compared with image 502,the predefined regions 107 have moved to a different position, fartherright in the frame than in image 501. When such images are viewedsuccessively as video, the predefined regions 107 will appear to blinkacross the screen. This is indicative of the input frequency not beingsynchronized with the image capture device.

Comparing image 503 with image 504, the same is true—the predefinedregions are in different positions. This is also the case when comparingimage 505 and image 506. Thus, the input frequency may again beadjusted.

When comparing image 505 to image 506, the predefined regions 107 areactive at substantially the same position in each image. When suchimages are viewed continuously, as video, the predefined regions 107appear to momentarily stand still, indicating that the input frequencyand liquid crystal device (101) are synchronized with the image capturedevice (401). Where this is the case, measurements such as exposureduration and shutter frequency may be obtained.

Turning now to FIG. 6, illustrated therein is one embodiment of a methodfor determining a continuous shutter rate using the testing apparatus(100) in accordance with the invention. Continuous shutter rate is therate at which multiple images may be obtained from the image capturedevice (401). For example, when a digital camera is placed in burstmode, the camera may take between two and ten images continuously. Therate at which this may occur is dependent upon several factors. Onesignificant factor is the metering that must occur when the imagecapture device (401) sets aperture and exposure. Metering is dependentupon the ambient light, which is why the testing apparatus (100) inaccordance with the invention is useful for making such measurements.

At step 601, the image capture device (401) is aimed at the subject(402). Where required, the subject (402) may be illuminated such that alevel of subject illuminance is above or below a predetermined number offootcandles as required by a particular test at step 602. The liquidcrystal device (101) is placed between the subject (402) and the imagecapture device (401) at step 603. As with FIG. 1 above, in oneembodiment, the liquid crystal device (101) includes the array of pixels(102) that are capable of segmentation into a plurality of thepredefined regions (107), individually and sequentially, in a sweeppattern in accordance with an input frequency.

At step 604, the liquid crystal device (101) is actuated, therebycausing the predefined regions (107) to begin sweeping across thedevice. At step 605, the input frequency is set. At step 606, the imagecapture device (401) begins capturing at least one image. Wheresynchronization is required, the image capture device (401) may capturea plurality of images.

Where synchronization is required, decision 607 determines whether thepredefined regions (107) are at substantially the same position fromframe to frame. Where they are not, the input frequency is adjusted atstep 608 until one of the plurality of the predefined regions (107) isactive at substantially the same position in at least two imagesselected from the plurality of images. Where the predefined regions(107) are stable, the continuous shutter rate may be determined simplyby determining the input frequency from the adjustable frequencygenerator (111).

In one embodiment, where the liquid crystal device (101) is coupled to aphotodetector (113), the step of adjusting the frequency generator, i.e.step 608, may be performed by providing a strobe flash having a selectedfrequency. By adjusting the frequency of the strobe flash, the inputfrequency is adjusted, as the input frequency is proportional to thestrobe flash frequency in one embodiment. Adjustment of the strobe flashfrequency provides an alternate means of synchronizing the predefinedregions (107) with the image capture device (401).

Turning now to FIG. 7, illustrated therein is one embodiment of a methodfor determining a duration of exposure associated with the image capturedevice (401) by using the testing apparatus (100) in accordance with theinvention. At step 701, the image capture device (401) is aimed at thesubject (402). At step 702, where required, the subject is illuminatedsuch that the subject illuminance is at the required footcandle level.At step 703, the liquid crystal device (101) having an array of pixelscapable of segmentation by the liquid crystal device driver (105) into aplurality of predefined regions, individually and sequentially, in asweep pattern, is placed between the subject (402) and the image capturedevice (401). At step 704, the liquid crystal device (101) is actuated.

At step 705, the adjustable frequency generator (111) is set to providean input frequency to the liquid crystal display driver (105). At step706, the image capture device (401) begins taking at least one image. Atstep 707, the number of active predefined regions (107) appearing in oneof the images selected during synchronization is determined.

At decision 708, one may determine whether a satisfactory resolution hasbeen achieved. Where it has not, at step 709, the adjustable frequencygenerator (111) may be adjusted until satisfactory exposure resolutionis achieved. At step 710, exposure is determined by multiplying thenumber of predefined regions (107) appearing in the image by an activeperiod associated with the predefined regions (107).

Turning now to FIG. 8, illustrated therein is one embodiment of a methodfor determining a lag time between a flash exposure and a correspondingimage capture in the image capture device (401), the method employingthe testing apparatus (100) in accordance with the invention. In thismethod, the liquid crystal device driver (105) is configured to beginsweeping predefined regions (107) across the liquid crystal device (101)upon receipt of light by the photodetector (113) from the flash (403).

At step 801, the image capture device (401) is aimed at the subject(402). At step 802, where required, the subject (402) may beilluminated. At step 803, the liquid crystal device (101) is positionedbetween the subject (402) and the image capture device (401). At step804, the photodetector (113) is armed so as to begin sweeping thepredefined regions (107) across the liquid crystal device (101) uponreceipt of light from the flash (403).

At steps 805 and 806, the flash and image capture are initiated. Onconventional digital cameras, this may be accomplished simply bypressing the shutter release button. As there is a finite lag betweenflash and image capture, some of the predefined regions (107) will sweepacross the liquid crystal device (101) between the time the flash (403)pops and the time the image is captured. To determine this time, at step807, the number of predefined regions (107) appearing in an image isdetermined. To calculate time, the number of predefined regions (107)appearing in the image is multiplied by a predefined region activeperiod at step 808.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Thus, while preferred embodiments of the invention havebeen illustrated and described, it is clear that the invention is not solimited. Numerous modifications, changes, variations, substitutions, andequivalents will occur to those skilled in the art without departingfrom the spirit and scope of the present invention as defined by thefollowing claims. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention.

1. An apparatus for measuring one of a duration of exposure and acontinuous shutter speed of an image capture device, the apparatuscomprising: a. a transparent liquid crystal device comprising an arrayof pixels, the transparent liquid crystal device having a device width;b. a liquid crystal device driver configured to actuate any of aplurality of subsets of the array of pixels individually, wherein theliquid crystal device driver actuates the plurality of subsetsindividually and sequentially in a sweep pattern in accordance with aninput frequency; and c. an adjustable frequency generator configured todeliver the input frequency to the liquid crystal device driver.
 2. Theapparatus of claim 1, wherein the plurality of subsets define aplurality of predefined regions, wherein each of the plurality ofpredefined regions comprises one of columns having a predeterminedcolumn length and a predetermined column width and rows having apredetermined row length and a predetermined row width.
 3. The apparatusof claim 2, wherein the plurality of predefined regions comprisecolumns, wherein the predetermined column width is less than or equal toa product of the device width, the input frequency and an exposure timemeasurement resolution.
 4. The apparatus of claim 3, wherein theexposure time measurement resolution is between 1 millisecond and 1second.
 5. The apparatus of claim 1, wherein when any of the pluralityof subsets is active, the any of the plurality of predefined regions isopaque.
 6. The apparatus of claim 1, further comprising graphicalindicia disposed on the transparent liquid crystal device.
 7. Theapparatus of claim 1, wherein the liquid crystal device driver isfurther configured to present graphical indicia by actuating selectedpixels of the transparent liquid crystal device.
 8. The apparatus ofclaim 1, further comprising a photodetector, wherein the liquid crystaldevice driver is responsive to the photodetector.
 9. The apparatus ofclaim 8, wherein the adjustable frequency generator is responsive to thephotodetector, such that the input frequency is proportional to a flashfrequency received by the photodetector.
 10. A system for measuring oneof a duration of exposure and a continuous shutter speed of an imagecapture device, the system comprising: a. a transparent liquid crystaldevice comprising an array of pixels disposed between the image capturedevice and a subject; b. a liquid crystal device driver configured toselectively actuate the array of pixels in a plurality of predefinedregions, individually and sequentially, in a sweep pattern in accordancewith an input frequency; and c. an adjustable frequency generatorconfigured to deliver the input frequency to the liquid crystal devicedriver.
 11. The system of claim 10, wherein when any of the pluralitypredefined regions is active, the any of the plurality of predefinedregions is opaque.
 12. A method for determining a continuous shutterrate associated with an image capture device, the method comprising thesteps of: a. aiming the image capture device at a subject; b. placing atransparent liquid crystal device between the image capture device andthe subject, the transparent liquid crystal device comprising an arrayof pixels, the transparent liquid crystal device having a liquid crystaldevice driver configured to actuate the array of pixels in a pluralityof predefined regions, individually and sequentially in a sweep pattern,in accordance with an input frequency received from an adjustablefrequency generator; c. causing the image capture device to capture aplurality of images; and d. adjusting the adjustable frequency generatoruntil one of the plurality of predefined regions is active atsubstantially a same position in at least two consecutive imagesselected from the plurality of images.
 13. The method of claim 12,further comprising the step of determining from the adjustable frequencygenerator the continuous shutter rate.
 14. The method of claim 12,wherein the adjustable frequency generator comprises a photodetector,further wherein the step of adjusting the adjustable frequency generatorcomprises the step of providing a strobe flash having a selectedfrequency to the photodetector.
 15. The method of claim 12, furthercomprising the step of illuminating the subject such that a level ofsubject illuminance is less than a predetermined number of footcandles.16. A method for determining a duration of exposure associated with animage capture device, the method comprising the steps of: a. aiming theimage capture device at a subject; b. placing a transparent liquidcrystal device between the image capture device and the subject, thetransparent liquid crystal device comprising an array of pixels, thearray of pixels being capable of segmentation into a plurality ofpredefined regions, individually and sequentially, in a sweep pattern inaccordance with an input frequency received from an adjustable frequencygenerator; c. causing the image capture device to capture at least oneimage; and d. determining a number of active predefined regionsappearing in the at least one image; and e. multiplying the number ofactive predefined regions by an active period for each of the pluralityof predefined regions.
 17. The method of claim 16, wherein the step ofcausing the image capture device to capture the at least one imagecomprises causing the image capture device to capture a series ofimages, further comprising the step of adjusting the adjustablefrequency generator until at least one of the plurality of predefinedregions is active at substantially a same position in at least twoconsecutive images selected from the series of images.
 18. The method ofclaim 17, wherein the at least one image is selected from the at leasttwo consecutive images.
 19. A method of determining a lag time between aflash exposure and an image capture in an image capture device, themethod comprising the steps of: a. placing a transparent liquid crystaldevice before the image capture device, the transparent liquid crystaldevice comprising a photodetector and an array of pixels, the array ofpixels being capable of segmentation into a plurality of predefinedregions, individually and sequentially, in a sweep pattern in responseto the photodetector; b. causing the image capture device to actuate aflash and capture at least one image; and c. determining a number ofactive predefined regions appearing in the at least one image.
 20. Themethod of claim 19, further comprising the step of multiplying thenumber of active predefined regions by an active period to determine thelag time.